Debbie Adlam is calling for a minimum jail term of 20 years for anyone who kills an officer, with no chance of parole during that time.
Driver Henry Long, 19, was handed a 16 year jail sentence while passengers Jessie Cole and Albert Bowers, both 18, each received 13 years.
Henry Long, 19, Jessie Cole, 18, and Albert Bowers, 18, were cleared of murder but still face years in jail for manslaughter.
Mr Justice Edis has discharged the jury and adjourned the Old Bailey trial with a “heavy heart” after three jurors went into self-isolation.
The 28-year-old Thames Valley Police officer was dragged behind a car for more than a mile when he was killed last year, a court has heard.
Henry Long, 18, has denied murder but pleaded guilty to the manslaughter of PC Harper, who was killed while on duty in August last year.
A 20-year-old man accused of murdering PC Andrew Harper had the charge against him dropped during a hearing at the Old Bailey today.
An 18-year-old and two 17-year-olds have been charged with murder following the death of the Thames Valley Police officer.
Four males have been arrested on suspicion of murder and theft after new evidence emerged in the investigation into PC Harper's death.
Jed Foster, the man accused of murdering PC Andrew Harper, is yet to enter his plea and will face trial in January.
Jed Foster, 20, has denied any involvement in the death of PC Andrew Harper, who was killed while performing his duties in Berkshire.